Severe orbital hematoma with third eyelid swelling and prolapse following a blind maxillary nerve block in a horse

Abstract

A 20-year-old quarter horse gelding was presented for routine dental examination. Periodontal disease and luxation of tooth 108 was diagnosed and oral extraction was planned. After an unsuccessful blind maxillary nerve block, it was elected to perform the procedure under total intravenous anesthesia. Following recovery, a focal superficial corneal ulcer, severe retrobulbar swelling, mild exophthalmos, and marked swelling and prolapse of the third eyelid (nictitating membrane) were observed. Clinical signs persisted beyond 48 h despite the use of systemic anti-inflammatories and topical ocular anti-inflammatories and antibiotics. A temporary tarsorrhaphy was subsequently done at 48 h and the horse was discharged after 5 d of hospitalization and regression of clinical signs. Although it is very useful for easing dental extractions, the blind maxillary nerve block is associated with potential complications due to inadvertent vascular puncture. This case report describes a rare complication of prolapse of the third eyelid in a horse after a maxillary nerve block and successful treatment with a temporary tarsorrhaphy.

Key clinical message:

This case report explains how nictitating membrane swelling and prolapse can occur following a blind maxillary nerve block in the horse and describes treatment with a temporary tarsorrhaphy.

Local anesthetics are invaluable tools in veterinary medicine that prevent the transmission of noxious stimuli through sensory nerves. The maxillofacial region in the awake animal is particularly sensitive to noxious stimuli, thus making desensitization of the surgical site and associated structures an integral part of a multimodal anesthetic approach during dental surgery. Desensitization of a nerve can prevent noxious stimuli and enhance patient compliance, thereby contributing to a successful and efficient procedure (1).

The maxillary nerve and its branches provide sensation to the paranasal sinus mucosa, maxillary cheek teeth, incisors, and associated gingiva (2); desensitization of this nerve can facilitate extraction of maxillary cheek teeth. Local anesthesia in combination with sedation and systemic analgesia can allow clinicians to perform standing procedures and avoid potential risks and complications of general anesthesia. The maxillary nerve can be desensitized where it passes through the pterygopalatine fossa between the zygomatic arch and the mandible (3).

The relatively simple procedure of introducing a local anesthetic around the maxillary nerve is complicated by the close proximity of adjacent vasculature, including the infraorbital artery, deep facial vein, and descending palatine artery (4). Complications may arise if these vessels are punctured or lacerated by the needle. Hematoma formation, orbital prolapse/exophthalmos, Horner’s syndrome, and even temporary blindness have been reported following maxillary nerve blocks (1,2,5). The purpose of this case report is to describe what the authors believe is the first documented case of third eyelid swelling and prolapse resulting from a blind maxillary nerve block complication in an equine.

Case description

A 20-year-old quarter horse gelding, weighing ~450 kg and with a thin body condition score of 3/9 (6), was presented to the Western College of Veterinary Medicine (Saskatoon, Saskatchewan) Equine Field Service for an oral examination on the home farm of the horse. There was no history of previous dental examinations and the owners reported no issues except that the horse was “strong in the bridle.”

The horse was sedated with a combination of 0.03 mg/kg acepromazine, 0.33 mg/kg xylazine, and 0.007 mg/kg butorphanol, IV. A McPherson speculum was placed in the mouth and an oral examination revealed a diastema between teeth 108 and 109 with feed packing and a foul odour. Tooth 108 was loose, with ~3 mm of movement of the crown in any direction. Abnormalities on radiographs of the maxillary cheek teeth included the diastema between teeth 108 and 109. The surrounding alveolar bone of teeth 108 and 109 was sclerotic and there were apical leucencies along the rostral and caudal roots of 108. The radiographic interpretation was an apical infection or abscess of tooth 108.

A dental float (crown odontoplasty) was attempted following additional administration of detomidine (0.0044 mg/kg, IV, twice). The horse was irritable and was unwilling to allow the floating procedure to continue. Phenylbutazone (4 mg/kg, IV) was administered to treat suspected dental pain.

Extraction of tooth 108 was scheduled for the following day. Regional anesthesia of the right maxillary nerve was attempted to desensitize the teeth and gingiva of the 100-series dental arcade. The skin was aseptically prepared with 2% chlorhexadine soap and alcohol. A spinal needle (22 G, 3.5 inches) was inserted immediately ventral to the right zygomatic process and advanced rostrally and ventrally in the direction of the 211 molar (7). Blood was obtained from the needle hub before achieving contact with the palatine bone. Consequently, the needle was removed, and local anesthetic was not administered. Compression with gauze was placed at the needle site following its removal and was held until the bleeding at the skin ceased. The horse was subsequently placed under total IV general anesthesia during extraction of the tooth and completion of the odontoplasty. The horse was anesthetized on the same day, in a 12 × 12-foot box stall with a deep bedding of wood shavings. A 14 G, 5.25-inch catheter was placed aseptically in the left jugular vein. General anesthesia was induced with 1.1 mg/kg xylazine, 2.2 mg/kg ketamine, and 0.022 mg/kg diazepam, IV through the catheter, and right lateral recumbency was acheived. Tooth 108 was successfully extracted with molar extractors and minor lateral force. The dental float was completed with an electric rotary dental float. The entire procedure took ~20 min and the horse recovered uneventfully from anesthesia within the hour. Immediately following recovery from anesthesia, swelling of the right retrobulbar region, protrusion of the third eyelid, and mild exophthalmos of the right eye were observed (Figure 1). A 1-centimeter, superficial corneal ulcer of the right eye was diagnosed via fluorescein stain.

Figure 1.

Observed retrobulbar swelling, mild exophthalmos, swelling, and prolapse of the third eyelid in a 20-year-old quarter horse gelding.

Dexamethasone (25 mg) was administered IV to decrease inflammation. Diclofenac (0.2 mL) and ciprofloxacin (0.2 mL) ophthalmic solutions were administered topically to the right eye. Sterile gauze soaked in sterile saline and covered in ophthalmic gel lubricant was placed over the protruding third eyelid and secured with a head bandage to protect the exposed third eyelid. The owner was instructed to continue to treat the right eye with diclofenac (2 drops, q8h) and ciprofloxacin (2 drops, q6h), replace the bandage as needed, and administer phenylbutazone (4 mg/kg, PO, q24h) for 4 to 5 d.

As limited improvement was achieved after 48 h, the horse was referred for an ophthalmology consultation at the Western College of Veterinary Medicine Large Animal Clinic. The horse was sedated with 0.33 mg/kg xylazine and 0.007 mg/kg butorphanol, IV, and line-blocks with 2% lidocaine HCl were placed in the upper and lower eyelids to facilitate the ophthalmic examination and treatment. The diagnoses of corneal ulceration and third eyelid swelling and protrusion were confirmed by a Diplomate of the College of Veterinary Ophthalmologists. A partial temporary tarsorrhaphy was recommended and completed by placement of 2 4-0 polybutester monofilament sutures in a horizontal mattress pattern, with stents centrally over the right eye (Figure 2). The nasal and temporal aspects of the eyelid margins were left open to facilitate assessment and treatment. The right eyelids were covered with silver sulfadiazine cream and a bandage to protect from infection and trauma.

Figure 2.

Appearance of the horse’s eye immediately following the tarsorrhaphy placement.

A subsequent oral examination under sedation with xylazine and butorphanol, IV, revealed malodor from the alveolar socket of tooth 108. The horse’s mouth was rinsed with chlorhexidine solution. Trimethoprim sulfadiazine (30 mg/kg, PO, q12h for 5 d) was prescribed to treat the alveolar infection. Flunixin meglumine (1.1 mg/kg, IV, q24h) replaced phenylbutazone for pain management. Topical corneal treatment was continued as previously described, along with daily bandage changes. Topical medications were administered at the medial or lateral canthus of the eye. The horse remained in hospital for 5 d. On the 4th day of hospitalization, 1 tarsorrhaphy suture was removed and diclofenac was discontinued. Before discharge, the tarsorrhaphy was completely removed and the third eyelid remained in a normal position. Repeat fluorescein staining of the right eye revealed resolution of the corneal ulcer. A repeat oral examination under standing sedation with xylazine and butorphanol, IV, was conducted before discharge, and the alveolar socket at tooth 108 was determined to be healing appropriately.

Discussion

Clinicians with limited experience performing the maxillary nerve block commonly place the needle inaccurately (8). This inaccuracy can cause trauma to surrounding structures and cause complications, as previously described. In this case, a clinician who was inexperienced in placing dental nerve blocks punctured a vessel during needle insertion, as indicated by blood flow through the needle. The vessel punctured was likely the deep facial vein, the maxillary artery, or both. These vessels were likely involved due to their proximity to the maxillary nerve as it enters the pterygopalatine fossa as well as the directionality of the needle taken in the blind approach that was used. The close proximity of the vasculature and direction of the needle can be seen in Figure 3.

Figure 3.

Photograph of the cadaveric dissection of the horse, revealing the left maxillary nerve as it enters the pterygopalatine fossa (black dashed line) and the deep facial vein (white arrow) in proximity. The (*) symbol identifies the craniolateral border of the vertical ramus of the mandible.

When a vessel is contacted during a maxillary nerve block, a hematoma may form and then act as a space-occupying mass. Exophthalmos then results from increased pressure on the periorbital structures, displacing the globe from the orbit. In this case, swelling of the third eyelid also occurred, which contributed to its prolapse. This swelling was likely edema formation within the third eyelid due to the surrounding inflammation and the positioning during general anesthesia. Right lateral recumbency was not ideal in this case, but occurred because the general anesthesia was performed in the field, outside of controlled hospital settings.

Many causes of a prolapsed third eyelid have been reported. Prolapse of the third eyelid occurred in a case of an orbital abscess that resulted in periorbital inflammation, chemosis, and exophthalmos (9). Protrusion of the third eyelid can also occur passively, from enophthalmos. Enophthalmos occurs with ocular pain, space-occupying orbital lesions, and Horner’s syndrome. In this case, there is a small possibility that the needle used for preanesthetic sedation and total IV anesthesia caused trauma to the surrounding tissue in the neck and contacted the vagosympathetic trunk, resulting in Horner’s syndrome; however, this was considered less likely due to the presence of exophthalmos in the horse (5,10).

Tetanus and hyperkalemic periodic paralysis are also causes of bilateral prolapse of the third eyelid due to effects on ocular musculature (11,12). However, due to the patient history and unilateral nature of this case, these diseases were unlikely to have been causes.

Traditionally, the maxillary nerve would be desensitized blindly, without ultrasonographic visualization (13). However, an ultrasound-guided approach can be particularly useful in assisting with maxillary nerve blocks. Ultrasound imaging allows the clinician to visualize the surrounding facial vasculature and therefore greatly reduce the risk of vessel puncture and perineural trauma (5). Various ultrasonographic techniques have been described (4,13,14). Modified blind techniques have also been described to avoid the deep vascular region around the maxillary nerve. The maxillary nerve can be desensitized by depositing local anesthetic in the extraperiorbital fat pad superficial to the vascular plexus (5). At a depth of 38 to 50 mm, just past the deep fascial plane of the maseter muscle, anesthetic solution diffuses deeper through the adipose tissue that surrounds the nerve (15,16). This technique would have been a safer method to use in this case, as no ultrasound equipment was available. The clinician carrying out the procedure was inexperienced in performing dental nerve blocks and chose the blind method as a learning experience.

Any time a vessel is punctured during a dental nerve block procedure, elevation of the head and compression at the injection site should be implemented to help reduce the severity of a potential hematoma. In this case, the horse was placed in lateral recumbency following vessel puncture, which likely contributed to the severity of the hematoma formation and related complications. Completion of the dental extraction took precedence in this case over consideration for the punctured vessel due to the severe reaction the horse displayed when the tooth was manipulated and its thin body condition during the winter months. Elevation of the head by keeping the horse standing would have been the best choice for prevention or treatment of the hematoma following inadvertent vessel puncture.

This case report highlighted risks associated with the blind approach of the maxillary nerve block and the treatment of swelling and prolapse of the third eyelid using temporary tarsorrhaphy. The blind approach may need to be used in cases where ultrasound equipment is unavailable or there is skin pathology such as a sarcoid or melanoma in the location of needle insertion for the extraperiorbital fat pad technique. This case demonstrated that any puncture to a vessel while performing this block can lead to serious complications. General anesthesia was considered to be the least painful way to complete the dental extraction in this horse, but anesthetizing the horse immediately after vessel puncture likely contributed to the swelling and prolapse of the third eyelid. This complication may have been avoided by using the extraperiorbital fat pad or ultrasound-guided technique of the maxillary nerve block and elevating the head following inadvertent vessel puncture. CVJ